Have you ever gone into an underground mine? If you have, you might have felt that it got warm as you descended into the ground. This is exactly what happens in the Earth: It gets warmer and warmer and warmer.

For every kilometer that you descend into the Earth, the temperature increases by ~25 °C (or 45 °F). Therefore, 5 km below the Earth, the temperature can be around 125 °C or 257 °F – beyond the boiling point of water. As you go deeper, the temperature still increases. Look at the graph that I added.

It shows a temperature profile through the first 250 m below Jericho (in Palestine). You can ignore all the details, just look at the bold red line. Now you can read the depth on the y axis (the downward axis) and the temperature on the x axis (the axis at the top). You can see that the temperature gets up to c.a. 1300 °C at 250 km.

If you go down through an ocean rather than such a continent, you might be at 1300°C after just ~100 – 125 km. After this, the temperature still increases and at the center of the Earth, you get to temperatures bigger than 5000°C – that is similar to the surface of the sun… You might know that the core of the Earth is made of Iron. At this temperature the iron would easily melt. However, pressure also changes:

The pressure is essentially the weight of the overlying material. As you go into the Earth, imagine piling kilometers and kilometers of rock on top of you. So, the pressure rises and rises and at the core of the Earth, the pressure is more than 3 million times the pressure of the atmosphere. Because of this high pressure, the iron in the core cannot melt and behaves as if it were solid, even though it is more than 5000°C hot. Let’s say, it wouldn’t be very pleasant to be down there…